fix: unbatch RPC calls and fix UI warning

Description

We had an outage on the Reserve site last night, which seems to be caused by Infura timing out on our batched RPC calls. It's intermittent and probably due to some internal scaling/infrastructure changes happening there.

I've removed the batching. But to improve performance and loading time and to get things in line, I suggest migrating all ethers and contractkit usage to viem so we can (easily) make use of multicall to not just batch at the RPC level but actually batch reads into a single RPC call, reducing the load.

Other changes

Removed price loading via the exchange - no longer working
Fixed a React key issue

Tested

Yes

Related issues

N/A

Backwards compatibility

N/A

Documentation

N/A

mento-protocol / reserve-site